The present invention relates to an indwelling stent for use in improving constriction occurred in a living organism such as blood vessel, bile duct, trachea, esophagus, urethra, other organs, etc.
A stent is a generally tubular tool having the function of maintaining a blood vessel or other incised lumen part in an opened state, and is used for improving stenosis of a blood vessel or the like.
Stents are classified, by the function and indwelling method thereof, into self-expandable stents and balloon expandable stents. The balloon expandable stent does not have a self-expanding function, and is used in such a manner that the stent is inserted into a target site, then a balloon is located inside the stent, and the balloon is inflated to expand (plastically deform) the stent by the inflation force of the balloon, thereby bringing the stent into close contact with the inside surface of the target site and fixing the stent there. In this type of stent, the operation of expanding the stent is needed.
A balloon expandable stent has been proposed, for example, in Japanese Patent Laid-open No. 2002-172176 by the present applicant.
The stent disclosed in FIGS. 4, 5 and 6 in the publication is formed in a roughly tubular shape, has a diameter allowing for insertion into a lumen in a living organism, and is expandable when radially outward forces are exerted thereon from the inside of the tubular shape.
The stent comprises a plurality of annular units arranged in the axial direction of the stent, wherein the annular units each comprise a plurality of roughly polygonal filamentous members each of which has a multiplicity of filamentous bent portions and an opening so as to be expandable under radially outward forces and which are joined to each other through a plurality of joints so as to be annular in overall shape. Further, the stent comprises links by which the adjacent annular units are linked to each other through the joints thereof and which are so disposed as not to be continuous with the adjacent links, and a plurality of links are provided between the adjacent annular units at opposed positions or at substantially regular angular intervals around the stent axis.
As shown in FIGS. 4 and 5 and FIG. 6, which is a development of FIG. 4, of the publication, the stent comprises a plurality of the annular units arranged in the axial direction of the stent 10, each of the annular units comprising a plurality of the roughly polygonal filamentous members each of which is elongate in the axial direction of the stent and has filamentous bent portions and a central opening and which are arranged substantially on the circumference of a circle at substantially regular angular intervals around the stent axis, adjacent portions (side portions) in the circumferential direction of the roughly polygonal filamentous members being joined to each other through the joints. Further, the joints of one annular unit and the joints of the adjacent annular unit are linked by the links at two or more locations. From another point of view, the stent 10 is a tubular body composed by linking a multiplicity of the annular units through the links.
A balloon expandable stent has been proposed, for example, in U.S. Pat. No. 5,879,381 by the present applicant.
The stent disclosed in FIGS. 1 to 3 of the publication is a so-called balloon expandale stent which is formed in a roughly tubular shape, has a diameter allowing for insertion into a living organism, and is expandable when radially outward forces are exerted thereon from the inside of the tubular shape. As shown in FIGS. 1 to 3 of the publication, the stent includes annular units arranged in the axial direction of the stent, wherein each annular unit has four roughly elliptic or polygonal annular elements each of which is elongate in the axial direction of the stent and has a central opening and which are arranged substantially on the circumference of a circle at roughly regular angular intervals around the stent axis, adjacent portions (side portions) in the circumferential direction of the annular elements being joined to each other by joints. Further, the adjacent annular units are interconnected at their joints by at least one link.
In general, the balloon expandable stent is produced with a predetermined outside diameter by use of a pipe of a plastically deformable material, a balloon is disposed inside the stent, and the diameter of the stent is reduced by compressing from outside so as to mount the stent onto the balloon. The stents shown in the above-mentioned patent references have the merit that shape retention after expansion is good and the overall length is little changed upon expansion, and have a sufficient effect for dilation of a living organ.
Recently, however, there is a demand for a stent capable of indwelling in a smaller-diameter living organ, particularly, a smaller-diameter blood vessel or bile duct. In the stents disclosed in the above-mentioned patent references, the adjacent roughly polygonal filamentous members or the adjacent roughly elliptic or polygonal annular elements extend in directions orthogonal to the stent axis. Therefore, even though the polygonal filamentous members (polygonal annular elements) can be compressed, it is difficult for the joints to be compressed, so that reduction in diameter by compression is limited, and it is impossible to compress the stent to a sufficiently small diameter.